[aprssig] Packet test
scott at opentrac.org
scott at opentrac.org
Mon Nov 27 10:41:39 CST 2006
Destination address should start with AP. You can get a product identifier
from Bob if you don't want to use the generic APRS tocall. SSID value
should be whatever the user selects - the use of SSIDs for station type is
deprecated. You can hard-code the control byte to 0x03 and the PID to 0xf0.
I'd have to check on the address field C bits. I'm pretty sure I've got the
one on the tocall set to 1, and on the fromcall set to 0.
For the proper CRC-CCITT algorithm, check my page at
<http://n1vg.net/packet>. It lists the bitwise version of the algorithm,
and has a link to the reference I used for the OpenTracker. The bitwise
algorithm doesn't require any lookup tables and can be done with shifts and
XORs - it may not be as fast, but it's very compact.
What are you using for the AFSK modulation? Are you doing it in hardware or
Until I saw your email address, I didn't realize that you're in Santa
Barbara - I'm an hour up the road from you in Santa Maria. Do you know
Bruce Gordon, N6OLT? I've used his DF equipment for years.
If you want a lower traffic list for a peer review of your message, you
might try the APRSSPEC list. It's mostly just us developers over there, and
no one minds esoteric discussions of protocol details.
> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of R. Simmons
> Sent: Monday, November 27, 2006 7:20 AM
> To: post_message APRS
> Subject: [aprssig] Packet test
> To all :
> I am developing PIC code to send an APRS DF message, ( for a
> DF beacon )
> and I approaching completion... getting close to an "air test" of the
> software but still a few "loose ends" to clear up...
> Questions about a suitable destination address, the proper
> SSID values and
> C-bit values. Also, the AX.25 spec says the CRC bytes should
> be sent MSB
> first, but public code I have seen shows LSB is sent first,
> things like
> Any ( authoritative ) help would be appreciated, and a peer
> review of my
> intended message would also be appreciated. I can be
> contacted "off-forum"
> at this address : pelican2 at silcom.com
> DE WB6EYV / Bob S.
> aprssig mailing list
> aprssig at lists.tapr.org
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